Shower mixer leak question

I have an attic shower that's been leaking into the floor below for at least a year. I figured out it's not the drain but appears to leak from the plumbing/faucet when the shower is on. It's a single handle faucet, the kind that pulls to turn on and twists to mix. Is there a most likely cause of leaks in this sort of faucet? I know I need to take the plate off and take a look, but it;s good to be armed with the proper materials before I disturb a tenant.
The leaky ceiling below has been pulled down while that apartment has been empty . . .

You need to remove the access panel behind the faucet. If you don't have such a panel, you should make one. It's also possible that the shower arm is the cause of this leak (the curved pipe that the shower head is attached to). You need to remove the access panel, turn on the shower, and look for where it's leaking.

I have what appears to be a Price Pfister 'Pull and turn' shower handle mixer/faucet. Really cheap one with the clear plastic 'teardrop' shape. Well the bathtub is leaking so I took off the handle, the backing-plate and the chrome sleeve. Now I'm down to the copper 'plus' with the extra 'leg' pointing at me. There's a small tab in a slot and when I pull it up it comes out, seems to be a snap ring of sorts. I'm just not sure how to get the open/close mechanism out of the shaft after I've removed the snap-ring. Seems to me the only thing to do is to get a wrench on the pivot shaft sticking out and go anti-clockwise on it. I'm a little nervous as the unit I'm messing with is part of a whole copper 'tree' that goes to the shower and tap and hot and cold.

Don't want to get too Rambo on it and break it.

Already undid the outer screws (needless) and let the bracket fall into the wall. Doh!

Can anyone help me out please? Just need to know the method to get the on/off mechanism out of the tree. I have a photo I can post if that will help.

Luckily in my case the leak was at the front of the valve (but still in/behind the shower wall) and the greenboard just below it soaked up most of the water. There was some wood damage, but luckily the structure is still sturdy and only the braces between the studs to support the faucet need replacing. I may add more anyway though. There is only one slight soft spot in the ceiling below.

I also have a very similar valve as you describe it, but the picture is way different. I've just decided to sweat in a new valve rather than repair.

Don't know if this helps; feel free to comment.

Thanks,

T.

Oh yeah, I don't have an access panel at all either. I might be able to build one that a smaller person could squeeze through, but I don't think I'll do that until/unless necessary. They'd basically have to crawl under the sink and into the vanity and then through a hole in the side of the alcove under the sink; I already plan to just get a cabinet face and not have a full cabinet under there anyway. Even then access would be limited and awkward at best due to the fact that the plumbing wall of the shower is also the wall of a chase, so there are ducts, flues, and other plumbing tubes in the way. Might be worth it just to have a small hole that someone could at least look through and shine a light, if there is line-of-sight from under the vanity to the valve.

Here is the cast brass(?) tree. It has a lathed finished collar that is part of the cast. Here I'm shown pulling the snap-ring free... but what to do next? Do I need a special tool?

Click to expand...

You have to pull out the cartridge. Certain brands like Moen have their own special cartridge puller. Try grabbing onto the stem with a channel locks and pulling it out as smoothely as you can. Once it's off, bring it to a hardware store or plumbing supply house and match it up for replacement.